U.S. patent application number 14/169933 was filed with the patent office on 2014-08-07 for power supply system.
This patent application is currently assigned to BROTHER KOGYO KABUSHIKI KAISHA. The applicant listed for this patent is Katsumi INUKAI. Invention is credited to Katsumi INUKAI.
Application Number | 20140218827 14/169933 |
Document ID | / |
Family ID | 51259029 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140218827 |
Kind Code |
A1 |
INUKAI; Katsumi |
August 7, 2014 |
POWER SUPPLY SYSTEM
Abstract
A power supply system includes: a switching power supply; a
switching unit for switching a connection state between an AC power
supply and the switching power supply; an electricity storage unit;
an auxiliary power supply circuit for feeding charging current to
the electricity storage unit; a driving circuit for driving the
switching unit; a voltage detection circuit for detecting a voltage
of the AC power supply; and a control device configured to perform:
an overvoltage detection process of determining whether the AC
power supply is an overvoltage based on a detection value of the
voltage detection circuit; and a process of, in a case where an
overvoltage is detected, keeping the switching unit at a cutoff
state where the alternating current power supply and the switching
power supply are disconnected.
Inventors: |
INUKAI; Katsumi;
(Iwakura-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INUKAI; Katsumi |
Iwakura-shi |
|
JP |
|
|
Assignee: |
BROTHER KOGYO KABUSHIKI
KAISHA
Nagoya-shi
JP
|
Family ID: |
51259029 |
Appl. No.: |
14/169933 |
Filed: |
January 31, 2014 |
Current U.S.
Class: |
361/18 |
Current CPC
Class: |
G06F 1/26 20130101; H02H
7/1252 20130101; H02H 11/006 20130101; H02H 9/04 20130101; H02H
7/1213 20130101; G03G 15/80 20130101; H02H 7/1227 20130101; G06F
1/28 20130101 |
Class at
Publication: |
361/18 |
International
Class: |
H02H 11/00 20060101
H02H011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2013 |
JP |
2013-018217 |
Claims
1. A power supply system comprising: a switching power supply
configured to convert an alternating current voltage from an
alternating current power supply into a predetermined direct
current voltage and to output the direct current voltage; a
switching unit, which is provided between the alternating current
power supply and the switching power supply, and which is
configured to switch a connection state between the alternating
current power supply and the switching power supply; a control
device; an electricity storage unit configured to feed power to the
control device in a case where the switching power supply is at a
stop; an auxiliary power supply circuit, which is connected in
parallel with the switching power supply with respect to the
alternating current power supply, and which is configured to feed
charging current to the electricity storage unit; a driving circuit
configured to drive the switching unit in response to an
instruction output from the control device; and a voltage detection
circuit configured to detect a voltage of the alternating current
power supply, wherein the control device is configured to perform:
an overvoltage detection process of, when starting up the switching
power supply, determining whether the alternating current power
supply is an overvoltage based on a detection value of the voltage
detection circuit; and a process of, in a case where an overvoltage
is detected in the overvoltage detection process, keeping the
switching unit at a cutoff state where the alternating current
power supply and the switching power supply are disconnected.
2. The power supply system according to claim 1, wherein in a case
where the overvoltage is not detected while the process of keeping
the switching unit at the cutoff state is being executed, the
control device is configured to control the driving circuit to
switch the switching unit to a connection state where the
alternating current power supply and the switching power supply are
connected.
3. The power supply system according to claim 1, wherein the
auxiliary power supply circuit comprises: a pair of coupling
capacitors; and a bridge-type rectification circuit, which is
connected to the alternating current power supply through the pair
of coupling capacitors, and which is configured to rectify the
alternating current voltage from the alternating current power
supply, wherein the auxiliary power supply circuit is configured to
supply current, which is output from the bridge-type rectification
circuit, to the electricity storage unit as the charging current,
wherein the voltage detection circuit comprises: a detection
resistance that generates a voltage corresponding to the current
output from the bridge-type rectification circuit; and a detection
circuit configured to detect a voltage between both ends of the
detection resistance, and wherein the control device is configured
to compare the voltage between both ends of the detection
resistance, which is detected by the detection circuit, and a
threshold so as to determine whether the alternating current power
supply is an overvoltage.
4. The power supply system according to claim 3, further
comprising: a pulse signal output circuit configured to output a
pulse signal having a frequency corresponding to a power supply
frequency of the alternating current power supply, wherein the
control device is configured to change a value of the threshold
based on the frequency of the pulse signal.
5. The power supply system according to claim 4, wherein the pulse
signal output circuit comprises a switching element configured to,
by being switched an on/off state thereof depending on a value of
the current output from the bridge-type rectification circuit,
output the pulse signal having the frequency corresponding to the
power supply frequency of the alternating current power supply, and
wherein the control device is configured to change the value of the
threshold based on comparison of the frequency of the pulse signal
and the power supply frequency.
6. The power supply system according to claim 3, wherein the
detection circuit comprises a peak hold circuit and is configured
to detect a peak value of the voltage between both ends of the
detection resistance.
7. The power supply system according to claim 3, wherein the
detection circuit comprises an averaging circuit and is configured
to detect an average value of the voltage between both ends of the
detection resistance.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Japanese Patent
Application No. 2013-018217 filed on Feb. 1, 2013, the entire
subject-matter of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to a technology of protecting a
switching power supply from an overvoltage.
BACKGROUND
[0003] There has been disclosed a technology of detecting an
overvoltage of an AC input to thus cut off an AC line, thereby
protecting an electronic component such as a smoothing capacitor
provided at a primary side of a switching power supply.
SUMMARY
[0004] Illustrative aspects of the invention provide a technology
for protecting a switching power supply from an overvoltage.
[0005] According to one illustrative aspect of the invention, there
is provided A power supply system comprising: a switching power
supply configured to convert an alternating current voltage from an
alternating current power supply into a predetermined direct
current voltage and to output the direct current voltage; a
switching unit, which is provided between the alternating current
power supply and the switching power supply, and which is
configured to switch a connection state between the alternating
current power supply and the switching power supply; a control
device; an electricity storage unit configured to feed power to the
control device in a case where the switching power supply is at a
stop; an auxiliary power supply circuit, which is connected in
parallel with the switching power supply with respect to the
alternating current power supply, and which is configured to feed
charging current to the electricity storage unit; a driving circuit
configured to drive the switching unit in response to an
instruction output from the control device; and a voltage detection
circuit configured to detect a voltage of the alternating current
power supply. The control device may be configured to perform: an
overvoltage detection process of, when starting up the switching
power supply, determining whether the alternating current power
supply is an overvoltage based on a detection value of the voltage
detection circuit; and a process of, in a case where an overvoltage
is detected in the overvoltage detection process, keeping the
switching unit at a cutoff state where the alternating current
power supply and the switching power supply are disconnected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a block diagram showing an electrical
configuration of a printer according to a first illustrative
embodiment;
[0007] FIG. 2 is a circuit diagram of a power supply device, which
shows a switching power supply-side;
[0008] FIG. 3 is a circuit diagram of the power supply device,
which shows an auxiliary power supply circuit-side;
[0009] FIG. 4 is a circuit diagram showing a current path of
current Ip when there is no frame ground;
[0010] FIG. 5 shows waveforms of the current IP and a pulse signal
Sp when there is no frame ground;
[0011] FIG. 6 is a circuit diagram showing a current path of the
current Ip when there is a frame ground;
[0012] FIG. 7 shows waveforms of the current IP and the pulse
signal Sp when there is a frame ground;
[0013] FIG. 8 is a table showing a relation between a frequency of
the pulse signal Sp and a threshold;
[0014] FIG. 9 is a graph showing a temporal change of a peak value
Vp when there is no frame ground and a power supply frequency is 50
Hz;
[0015] FIG. 10 is a graph showing a temporal change of the peak
value Vp when there is no frame ground and the power supply
frequency is 60 Hz;
[0016] FIG. 11 is a graph showing a temporal change of the peak
value Vp when there is a frame ground and the power supply
frequency is 50 Hz;
[0017] FIG. 12 is a graph showing a temporal change of the peak
value Vp when there is a frame ground and the power supply
frequency is 60 Hz;
[0018] FIG. 13 is a flowchart showing a protection sequence of a
switching power supply;
[0019] FIG. 14 is a circuit diagram of a power supply device
according to a second illustrative embodiment, which shows the
auxiliary power supply circuit-side; and
[0020] FIG. 15 is a circuit diagram of a power supply device
according to a third illustrative embodiment, which shows the
auxiliary power supply circuit-side.
DETAILED DESCRIPTION
<General Overview>
[0021] The above-described related-art technology has some
disadvantages. For example, according to the above-described
related-art technology, it is not possible to detect the
overvoltage until an AC input to a power supply circuit, which is a
protection target, is made. Hence, when a large overvoltage is
generated, the detection thereof may be delayed and the smoothing
capacitor may not be protected, so that a specific measure is
needed.
[0022] Therefore, illustrative aspects of the invention provide a
technology for protecting a switching power supply from an
overvoltage.
[0023] According to one illustrative aspect of the invention, there
is provided A power supply system comprising: a switching power
supply configured to convert an alternating current voltage from an
alternating current power supply into a predetermined direct
current voltage and to output the direct current voltage; a
switching unit, which is provided between the alternating current
power supply and the switching power supply, and which is
configured to switch a connection state between the alternating
current power supply and the switching power supply; a control
device; an electricity storage unit configured to feed power to the
control device in a case where the switching power supply is at a
stop; an auxiliary power supply circuit, which is connected in
parallel with the switching power supply with respect to the
alternating current power supply, and which is configured to feed
charging current to the electricity storage unit; a driving circuit
configured to drive the switching unit in response to an
instruction output from the control device; and a voltage detection
circuit configured to detect a voltage of the alternating current
power supply. The control device may be configured to perform: an
overvoltage detection process of, when starting up the switching
power supply, determining whether the alternating current power
supply is an overvoltage based on a detection value of the voltage
detection circuit; and a process of, in a case where an overvoltage
is detected in the overvoltage detection process, keeping the
switching unit at a cutoff state where the alternating current
power supply and the switching power supply are disconnected.
[0024] In the above configuration, when an overvoltage of the
alternating current power supply is detected, the alternating
current power supply and the switching power supply are kept at a
disconnected state. For this reason, the overvoltage is not applied
to the switching power supply, so that the switching power supply
can be protected from the overvoltage.
[0025] Regarding illustrative embodiments of the power supply
system, following configurations are preferable.
[0026] In a case where the overvoltage is not detected while the
process of keeping the switching unit at the cutoff state is being
executed, the control device is configured to control the driving
circuit to switch the switching unit to a connection state where
the alternating current power supply and the switching power supply
are connected.
[0027] According thereto, in a case where the overvoltage is not
detected, it is possible to automatically start up the switching
power supply.
[0028] The auxiliary power supply circuit may comprise: a pair of
coupling capacitors; and a bridge-type rectification circuit, which
is connected to the alternating current power supply through the
pair of coupling capacitors, and which is configured to rectify the
alternating current voltage from the alternating current power
supply. The auxiliary power supply circuit may be configured to
supply current, which is output from the bridge-type rectification
circuit, to the electricity storage unit as the charging current.
The voltage detection circuit may comprise: a detection resistance
that generates a voltage corresponding to the current output from
the bridge-type rectification circuit; and a detection circuit
configured to detect a voltage between both ends of the detection
resistance. The control device may be configured to compare the
voltage between both ends of the detection resistance, which is
detected by the detection circuit, and a threshold so as to
determine whether the alternating current power supply is an
overvoltage.
[0029] According thereto, it is possible to configure the auxiliary
power supply circuit and the voltage detection circuit with
relatively simple circuits.
[0030] The power supply system may further comprise a pulse signal
output circuit configured to output a pulse signal having a
frequency corresponding to a power supply frequency of the
alternating current power supply. The control device may be
configured to change a value of the threshold based on the
frequency of the pulse signal.
[0031] A magnitude of the current flowing through the detection
resistance is changed depending on the power supply frequency of
the alternating current power supply. In this illustrative
embodiment, since the threshold is changed depending on the power
supply frequency of the alternating current power supply, it is
possible to correctly determine whether the alternating current
power supply is an overvoltage, irrespective of the power supply
frequency.
[0032] The pulse signal output circuit may comprise a switching
element configured to, by being switched an on/off state thereof
depending on a value of the current output from the bridge-type
rectification circuit, output the pulse signal having the frequency
corresponding to the power supply frequency of the alternating
current power supply. The control device may be configured to
change the value of the threshold based on comparison of the
frequency of the pulse signal and the power supply frequency.
[0033] The magnitude of the current flowing through the detection
resistance is changed depending on whether there is a frame ground.
In this illustrative embodiment, considering that a ratio of the
frequency of the pulse signal and the power supply frequency is
changed depending on whether there is a frame ground, the threshold
is changed depending on the ratio of the frequency of the pulse
signal and the power supply frequency. For this reason, it is
possible to correctly determine whether the alternating current
power supply is an overvoltage, irrespective of whether there is a
frame ground.
[0034] The detection circuit may comprise a peak hold circuit and
may be configured to detect a peak value of the voltage between
both ends of the detection resistance.
[0035] According thereto, compared to a configuration of
calculating an average, it is possible to detect the voltage
between both ends of the detection resistance in a short time.
[0036] The detection circuit may comprise an averaging circuit and
may be configured to detect an average value of the voltage between
both ends of the detection resistance.
[0037] According thereto, influences of noise during the detection
can be suppressed, so that it is possible to correctly detect the
voltage between both ends of the detection resistance.
[0038] According to the invention, it is possible to protect a
switching power supply from an overvoltage.
ILLUSTRATIVE EMBODIMENTS
First Illustrative Embodiment
[0039] A first illustrative embodiment of the invention will be
described with reference to FIGS. 1 to 13.
[0040] 1. Printer
[0041] FIG. 1 is a block diagram showing an electrical
configuration of a printer (which is an example of the `image
forming apparatus`) 1. The printer 1 has a printing unit 2, a
communication unit 3a, an image memory 3b and a power supply system
S. The power supply system S has a power supply device 10 and a
control device 100. The power supply device 10 is a power supply of
the printer 1 and feeds power to the printing unit 2, the
communication unit 3a, the image memory 3b and the control device
100.
[0042] The printing unit 2 has a photosensitive drum 2a, a charger
2b that executes a charging process of charging a surface of the
photosensitive drum 2a, an exposure device 2c that executes an
exposing process of forming an electrostatic latent image on the
surface of the photosensitive drum 2a, a developing device 2d that
executes a developing process of attaching developer on the
electrostatic latent image formed on the surface of the
photosensitive drum 2a to thereby form a developer image, a
transfer device 2e that executes a transfer process of transferring
the developer image to a recording medium and a fixing device 2f
that executes a fixing process of fixing the developer image
transferred onto the recording medium.
[0043] The printing unit 2 executes the charging process, the
exposing process, the developing process, the transfer process and
the fixing process, thereby executing a printing process of
printing print data on the recording medium. The communication unit
3a performs communication with an information terminal apparatus
such as a PC and receives a printing instruction or print data from
the information terminal apparatus. The image memory 3b temporarily
stores therein the print data received from the information
terminal apparatus.
[0044] When the communication unit 3a receives a printing
instruction and print data from the information terminal apparatus,
the control device 100 of the printer 1 enables the printing unit 2
to execute the printing process consisting of the charging process,
the exposing process, the developing process, the transfer process
and the fixing process, thereby printing the print data on the
recording medium. Incidentally, while an operating voltage of the
printing unit 2 is 24V, operating voltages of the communication
unit 3a, the image memory 3b and the control device 100 are
3.3V.
[0045] 2. Circuits of Power Supply System
[0046] First, a configuration of the power supply device 10 of the
power supply system S is described with reference to FIGS. 2 and 3.
The power supply device 10 has a switching power supply 20, a
backup capacitor CB that feeds power to the control device 100 when
the switching power supply 20 is at a stop, an auxiliary power
supply circuit 50, a relay 40, a pulse signal output circuit 60, a
voltage detection circuit 70 and a relay driving circuit 80.
Incidentally, the relay 40 is an example of the `switching unit` of
the invention and the relay driving circuit 80 is an example of the
`driving circuit` of the invention. Also, the backup capacitor CB
is an example of the `electricity storage unit` of the
invention.
[0047] FIG. 2 is a circuit diagram showing a configuration of the
switching power supply 20-side of the power supply system S. The
switching power supply 20 has a rectification smoothing circuit 21,
a transformer 23, an FET (Field Effect Transistor) 25, a
rectification smoothing circuit 27, a voltage detection circuit 29
and a control IC 30 that switching-controls the FET 25, and
converts and outputs an alternating current (AC) voltage, which is
input from an AC power supply 15, into a predetermined direct
current (DC) voltage.
[0048] The rectification smoothing circuit 21 is a so-called
capacitor input type and has a bridge diode D1 that rectifies the
AC voltage from the AC power supply 15 and a capacitor C1 that
smoothes the rectified voltage. The transformer 23 is provided at
an output-side of the rectification smoothing circuit 21 and an
input voltage Vin, which is obtained by rectifying and smoothing
the AC voltage, is applied to a primary coil N1 of the transformer
23.
[0049] The FET 25 is an N-channel MOSFET and has a drain D, which
is connected to the primary coil N1, and a source S, which is
connected to a reference potential of the primary-side. As an
on/off signal (PWM signal) is applied to a gate G from an output
port OUT of the control IC 30, the FET 25 becomes on/off at a
predetermined period. Thereby, the primary-side of the transformer
23 oscillates, so that a voltage is induced to a secondary coil N2
of the transformer 23.
[0050] Also, the primary-side of the transformer 23 is provided
with a voltage generation circuit 31. The voltage generation
circuit 31 rectifies and smoothes a voltage, which is induced to an
auxiliary coil N3 provided at the primary-side of the transformer
23, by a diode D2 and a capacitor C2. The voltage generation
circuit 31 becomes a power supply (about 20V) of the control IC
30.
[0051] The rectification smoothing circuit 27 is provided at a
secondary-side of the transformer 23 and has a diode D3 and a
capacitor C3. The rectification smoothing circuit 27 rectifies and
smoothes a voltage that is induced to the secondary coil N2 of the
transformer 23. Thereby, the switching power supply 20 outputs a
voltage of DC 24V through an output line Lo1.
[0052] As shown in FIG. 2, the output line Lo1 is branched into
three lines at a branch point J, and the respective branched lines
are provided with DC-DC converters 35, 37, respectively. The DC-DC
converter 35 drops an output voltage Vo1 of the switching power
supply 20 to 5V and outputs the same from an output line Lo2. Also,
the DC-DC converter 37 drops the output voltage Vo1 of the
switching power supply 20 to 3.3V and outputs the same from an
output line Lo3. Like this, the switching power supply 20 is
configured to output the three voltages of 24V/5V/3.3V.
[0053] Also, the voltage detection circuit 29 is provided between
the rectification smoothing circuit 27 and the branch point J of
the output line. The voltage detection circuit 29 detects a level
of the output voltage Vo1 (DC 24V) of the switching power supply 20
and has a pair of detection resistances R1, R2, a shunt regulator
Re and a light emitting diode LED1 serially connected to the shunt
regulator Re.
[0054] The detection resistances R1, R2 are provided between the
output line Lo1 and a reference potential SG (signal ground) of the
secondary-side and detect a divided voltage Vg that is obtained by
dividing the output voltage Vo1 by a resistance ratio. The shunt
regulator Re enables the current to flow in accordance with a level
difference between a reference voltage in the shunt regulator Re
and the divided voltage Vg. Thereby, the current is enabled to flow
through the light emitting diode LED1 and the light emitting diode
LED1 outputs a light signal having a light quantity corresponding
to the level difference between the reference voltage and the
divided voltage Vg.
[0055] The light emitting diode LED1 configures a photo-coupler
together with a photo transistor PT1 connected to a feedback port
FB of the control IC 30. For this reason, the light signal of the
light emitting diode LED1 is returned at the photo transistor PT1,
as an electric signal. Thereby, a signal (hereinafter, referred to
as a feedback signal), which indicates the level difference between
the reference voltage in the shunt regulator Re and the divided
voltage Vg, is input (fed back) to the feedback port FB of the
control IC 30.
[0056] As shown in FIG. 2, the control IC 30 has a power supply
port VCC that is connected to the voltage generation circuit 31, a
high voltage input port VH that is connected to a power supply line
through a resistance, the feedback port FB to which the feedback
signal is input, an output port OUT that outputs an on/off signal
(PWM signal) and an EN port to which a control signal is input.
[0057] The control IC 30 has a PWM comparator and an oscillation
circuit (not shown) that oscillates a triangular wave. When the
feedback signal is input to the feedback port FB, the control IC 30
generates a PWM signal in accordance with the feedback signal and
outputs the same to the gage G of the FET 25 through the output
port OUT. Thereby, the output voltage VO1 of the switching power
supply 20 is controlled to be a target voltage. In addition to
this, the control IC 30 stops and resumes the switching control
(the on/off control) of the FET 25, in response to the control
signal output from the control device 100, which will be described
later.
[0058] Also, as shown in FIG. 2, the relay 40 is provided between
the AC power supply 15 and the switching power supply 20.
Specifically, the relay 40 is provided on a line of a live LV-side
of a pair of power supply lines, i.e., two lines of the live
LV-side and a neutral NT-side connecting the AC power supply 15 and
the switching power supply 20. Incidentally, the live LV-side means
a non-ground-side and the neutral NT-side means a ground-side.
[0059] The relay 40 has a transfer contact point 41 and a driving
coil 43 that performs a switching of the transfer contact point 41.
The transfer contact point 41 has two fixed contact points 41a, 41b
and a moveable contact point 41c and switches a connection state
between the AC power supply 15 and the switching power supply 20.
That is, while the moveable contact point 41c is connected to the
switching power supply 20, the fixed contact point 41a is connected
to the AC power supply 15 and the fixed contact point 41b is not
connected.
[0060] For this reason, when the driving coil 43 is energized in a
forward direction (an A direction shown in FIG. 3) to thus close
the fixed contact point 41a, the power supply line of the live
LV-side is closed, so that the switching power supply 20 is
connected to the AC power supply 15. On the other hand, when the
driving coil 43 is energized in a reverse direction (a B direction
shown in FIG. 3) to thus close the fixed contact point 41b, the
power supply line of the live LV-side is opened, so that the
switching power supply 20 is disconnected from the AC power supply
15. Incidentally, the driving coils 43 shown in FIGS. 2 and 3 are
the same.
[0061] FIG. 3 is a circuit diagram of the auxiliary power supply
circuit 50, the pulse signal output circuit 60, the voltage
detection circuit 70 and the relay driving circuit 80 in the power
supply system S. The auxiliary power supply circuit 50 is a circuit
that is connected in parallel with the switching power supply 20
with respect to the AC power supply 15 and feeds charging current
to the backup capacitor CB.
[0062] Specifically, the auxiliary power supply circuit 50 has
coupling capacitors C4, C5 and a bridge-type rectification circuit
53. The coupling capacitor C4 is connected to a power supply line
AC_L of the live LV-side of the pair of power supply lines drawn
out from the AC power supply 15 and the coupling capacitor C5 is
connected to a power supply line AC_N of the neutral NT-side.
[0063] The rectification circuit 53 is a bridge diode (four
bridge-connected diodes D4 to D7), is connected to the AC power
supply 15 via the coupling capacitors C4, C5 and rectifies the AC
voltage from the AC power supply 15. Among the bridge diodes, a
connection point of the diode D6 and the diode D7 is connected to
the reference potential SG of the secondary-side through a
resistance R5. An output line Lo4 is drawn out from a connection
point of the diode D4 and the diode D5. The backup capacitor CB is
connected to the output line Lo4 of the rectification circuit 53
and the current rectified by the rectification circuit 53 is
supplied to the backup capacitor CB, as the charging current. In
this way, since the charging current is supplied to the backup
capacitor CB from the auxiliary power supply circuit 50, the backup
capacitor CB is charged even when the switching power supply 20 is
at a stop. Also, the backup capacitor CB is connected to the output
line Lo2 of 5V through a diode D9 and is also charged from the
switching power supply 20-side while the switching power supply 20
is operating. Incidentally, the other end of the backup capacitor
CB is connected to the reference potential SG (signal ground) of
the secondary-side through a resistance R3. Also, the backup
capacitor CB is connected in parallel with a zener diode Dz, so
that it stabilizes the charging voltage.
[0064] The pulse signal output circuit 60 is a circuit that outputs
a pulse signal Sp having a frequency corresponding to a power
supply frequency of the AC power supply 15 and has the resistance
R3, a transistor Q, a resistance R4 and a diode D8. The transistor
Q is an NPN transistor of which an emitter is connected to the
reference potential SG of the secondary-side and a collector is
connected to the output line Lo4 through the resistance R4. A base
is connected to a connection point of the backup capacitor CB and
the resistance R3. Also, the diode D8 has an anode that is
connected to the emitter of the transistor Q and a cathode that is
connected to the base of the transistor Q. Incidentally, the
transistor Q is an example of the `switching element` of the
invention.
[0065] The transistor Q becomes on when a voltage between the base
and the emitter exceeds a threshold voltage and becomes off when
the voltage between the base and the emitter becomes smaller than
the threshold voltage. The voltage between the base and the emitter
is changed in accordance with current Ip having a rectified
waveform and flowing through the resistance R3 via the
rectification circuit 53 at the AC power supply 15-side, and
becomes off (is on during the other time period) during a time
period for which the current Ip is smaller than a reference value,
as shown in FIG. 5 or 7. For this reason, the output of the pulse
signal output circuit 60, i.e., the output (a potential of the
collector) of the transistor Q becomes the pulse signal Sp
corresponding to the power supply frequency of the AC power supply
15. In this way, `the pulse signal output circuit 60 of the
invention is switched between the on state and the off state in
accordance with the value of the current (in this example, the
current Ip having the rectified waveform) output from the
bridge-type rectification circuit 53, so that a circuit including
the switching element (in this example, the transistor Q)
outputting the pulse signal Sp having a frequency corresponding to
the power supply frequency of the AC power supply 15 is
implemented.`
[0066] The output line (the output line drawn out from the
collector of the transistor Q) of the pulse signal output circuit
60 is connected to an input port P3 of a relay control block B2 of
the control device 100, so that the pulse signal Sp output from the
pulse signal output circuit 60 is input to the relay control block
B2.
[0067] Incidentally, the reference potential SG (signal ground) of
the secondary-side circuit (the auxiliary power supply circuit 50,
the pulse signal output circuit 60, the voltage detection circuit
70, the relay driving circuit 80, the control device 100 and the
like) is electrically connected to a metal frame (housing)
configuring the printer 1. If the metal frame (not shown) is not
grounded (hereinafter, there is no frame ground), the current Ip
flowing from the AC power supply 15 to the auxiliary power supply
circuit 50 flows along a path shown in FIG. 4, i.e., a path of the
AC power supply 15.fwdarw.the capacitor C4.fwdarw.the diode
D4.fwdarw.the detection resistance Ra.fwdarw.the capacitor CB or
zener diode Dz.fwdarw.the resistance R3.fwdarw.the resistance
R5.fwdarw.the diode D7.fwdarw.the capacitor C5.fwdarw.the AC power
supply 15 when the AC power supply 15 is a positive half wave, and
flows a path of the AC power supply 15.fwdarw.the capacitor
C5.fwdarw.the diode D5.fwdarw.the detection resistance
Ra.fwdarw.the capacitor CB or zener diode Dz.fwdarw.the resistance
R3.fwdarw.the resistance R5.fwdarw.the diode D6.fwdarw.the
capacitor C4.fwdarw.the AC power supply 15 when the AC power supply
15 is a negative half wave. Therefore, a full wave rectification
waveform is obtained. For this reason, as shown in FIG. 5, the
frequency of the pulse signal Sp output from the pulse signal
output circuit 60 becomes a double frequency of the power supply
frequency. In this case, since the current Ip flows via both the
coupling capacitors C5, C6, a circuit impedance is high and the
current value becomes small.
[0068] On the other hand, if the metal frame is grounded
(hereinafter, there is a frame ground), the above-described
secondary-side circuit is grounded via the frame ground (FG).
Therefore, in a case where there is the frame ground, the current
Ip flowing from the AC power supply 15 to the auxiliary power
supply circuit 50 flows along a path of FIG. 6, i.e., a path of the
AC power supply 15.fwdarw.the capacitor C4.fwdarw.the diode
D4.fwdarw.the detection resistance Ra.fwdarw.the capacitor CB or
zener diode Dz.fwdarw.the resistance R3.fwdarw.the AC power supply
15 only when the AC power supply 15 is a positive half period. For
this reason, when there is a frame ground, as shown in FIG. 7, the
frequency of the pulse signal Sp output from the pulse signal
output circuit 60 is the same as the power supply frequency. In
this case, since the current Ip flows only via the coupling
capacitor C4, the circuit impedance is low and an amount of the
current Ip becomes approximately twice as compared to the case
where there is no frame ground. Incidentally, whether or not to
ground the printer 1 may be determined by the user.
[0069] The voltage detection circuit 70 detects the voltage of the
AC power supply 15 and has the detection resistance Ra and a
processing circuit 75, as shown in FIG. 3. The detection resistance
Ra is provided on the output line Lo4 of the rectification circuit
53 and generates a voltage corresponding to the current I output
from the auxiliary power supply circuit 50, as shown in FIG. 3.
Incidentally, the processing circuit 75 is an example of the
`detection circuit` of the invention.
[0070] The processing circuit 75 has a subtraction circuit 76, an
amplification circuit 77 and a peak hold circuit 78. The processing
circuit 75 is input with respective voltages of both ends of the
detection resistance Ra through the two input lines, i.e., a
voltage of a point a shown in FIG. 3 and a voltage of a point b
shown in FIG. 3. The subtraction circuit 76 calculates a voltage
Vab between both ends of the detection resistance Ra by subtracting
the voltage of the point b from the voltage of the point a.
[0071] The voltage Vab between both ends, which is calculated by
the subtraction circuit 76, is amplified (four times, in this
example) by the amplification circuit and is then input to the peak
hold circuit 78. The peak hold circuit 78 detects a peak value Vp
of the voltage Vab between both ends after the amplification. The
output line of the voltage detection circuit 70 is connected to an
input port P4 of the relay control block B2 of the control device
100, so that the peak value Vp of the voltage Vab between both ends
of the detection resistance Ra is input to the relay control block
B2.
[0072] The relay driving circuit 80 is a circuit that drives
(energization-controls) the driving coil 43. The relay driving
circuit 80 has two PNP transistors Tr1, Tr2 and two NPN transistors
Tr3, Tr4.
[0073] As shown in FIG. 3, the transistor Tr1 and the transistor
Tr2 have emitters that are commonly connected to the backup
capacitor CB. On the other hand, the transistor Tr3 and the
transistor Tr4 have emitters that are commonly connected to the
reference potential SG of the secondary-side circuit. Collectors of
the transistor Tr1 and the transistor Tr3 are connected to each
other and collectors of the transistor Tr2 and the transistor Tr4
are connected to each other.
[0074] Also, connection lines are respectively drawn out from a
connection point of the transistor Tr1 and the transistor Tr3 and a
connection point of the transistor Tr2 and the transistor Tr4, and
the connection point of the transistor Tr1 and the transistor Tr3
is connected to one side of the driving coil 43 of the relay 40
through the connection line and the connection point of the
transistor Tr2 and the transistor Tr4 is connected to the other
side side of the driving coil 43. Among the four transistors Tr1,
Tr2, Tr3, Tr4, the transistor Tr1 and the transistor Tr4 configures
one set and the transistor Tr2 and the transistor Tr3 configures
one set.
[0075] When a driving signal (an on signal) is sent from the relay
control block B2 of the control device 100 to the relay driving
circuit 80, the on and off of the relay 40 can be switched. That
is, when the driving signal (an on signal) is output from a control
port P5 of the relay control block B2, the transistor Tr1 and the
transistor Tr4 become on and the current flows from the backup
capacitor CB to the driving coil 43 in the A direction shown in
FIG. 3. Thereby, the fixed contact point 41a is closed and the
relay 40 becomes on (the power supply line of the live LV-side is
closed).
[0076] On the other hand, when the driving signal (an on signal) is
output from a control port P6 of the relay control block B2, the
transistor Tr2 and the transistor Tr3 become on and the current
flows from the backup capacitor CB to the driving coil 43 in the B
direction shown in FIG. 3. Thereby, the fixed contact point 41b is
closed and the relay 40 becomes off (the power supply line of the
live LV-side is opened). Incidentally, since the relay driving
circuit 80 is connected to the output line Lo2 of 5V through the
diode D9, when the switching power supply 20 is operating, the
relay driving circuit 80 can operate by using the switching power
supply 20 as a power supply. Also, in this illustrative embodiment,
since a latching relay is used as the relay 40, it is possible to
configure the driving signal by the pulse signal.
[0077] The control device 100 has a main block B1 that controls the
printing unit 2 of the printer 1, and the relay control block B2.
The respective blocks B1, B2 can be configured by any one of one or
more CPUs, a hardware circuit such as an ASIC and a combination of
a CPU and a hardware circuit.
[0078] A power supply port P1 of the main block B1 is connected to
the output line Lo3 of the DC-DC converter 37 and is fed with the
power from the switching power supply 20 through the DC-DC
converter 37. Incidentally, the main block B1 is fed with the power
and thus operates only in an output mode where the switching power
supply 20 is at an output state, and when the switching power
supply 20 stops the output, the power feed is interrupted, so that
the main block B1 is at a stop.
[0079] The relay control block B2 switches the relay 40 through the
relay driving circuit 80. As described above, the relay control
block B2 is provided with the two control ports P5, P6. When the
driving signal is output from the control port P5, the relay
control block B2 can turn on the relay 40 (closes the fixed contact
point 41a), and when the driving signal is output from the control
port P6, the relay control block B2 can turn off the relay 40
(closes the fixed contact point 41b). Incidentally, since the relay
control block B2 uses the backup capacitor CB as a power supply,
the relay control block B2 can operate when the backup capacitor CB
is charged, even though the switching power supply 20 stops the
output.
[0080] 3. Protection of Switching Power Supply 20
[0081] In order to protect the switching power supply 20, it is
preferable that an overvoltage not be applied to the respective
electronic components such as the smoothing capacitor C1 provided
at the primary-side. In the power supply system S, when starting up
the switching power supply 20, the relay 40 is beforehand off, so
that the switching power supply 20 is cut off from the AC power
supply 15.
[0082] Then, based on the detection value (in this example, the
peak value Vp of the voltage Vab between both ends of the detection
resistance Ra) of the voltage detection circuit 70, it is
determined whether the AC input voltage from the AC power supply 15
is an overvoltage or not (one example of an overvoltage detection
process). When an overvoltage is not detected, the relay 40 becomes
on, so that the switching power supply 20 is connected to the AC
power supply 15 and the switching power supply 20 is thus
operated.
[0083] On the other hand, when an overvoltage is detected, the
relay 40 is kept at the off state and the switching power supply 20
is kept at the cutoff state from the AC power supply 15. Then, at
the time that the overvoltage is not detected, the relay 40 is
shifted to the on state, so that the switching power supply 20 is
connected to the AC power supply 15 and the switching power supply
20 is thus operated. In this way, the switching power supply 20 is
not applied with the overvoltage, so that the switching power
supply 20 can be protected from the overvoltage.
[0084] Also, as described above, since the circuit impedance is
changed depending on whether there is the frame ground, a magnitude
of the current flowing through the detection resistance Ra of the
voltage detection circuit 70 is changed even though the AC input
voltage (the power supply voltage of the AC power supply 15) is the
same. For this reason, when a threshold for determining the
overvoltage is fixed, it is possible to correctly determine whether
the AC input voltage is an overvoltage. Also, likewise, when the
power supply frequency of the AC power supply 15 is different, the
circuit impedance is changed. Therefore, the magnitude of the
current flowing through the detection resistance Ra of the voltage
detection circuit 70 is changed even though the AC input voltage
(the power supply voltage of the AC power supply) is the same. For
this reason, when a threshold for determining the overvoltage is
fixed, it is possible to correctly determine whether the AC input
voltage is an overvoltage.
[0085] Therefore, in this illustrative embodiment, the threshold
for determining whether the AC input voltage is an overvoltage is
changed depending on the frequency of the pulse signal Sp that is
output from the pulse signal output circuit 60. Specifically, in a
circuit example of the power supply device 10, as shown in FIG. 8,
in the case of a condition A, when the power supply voltage of the
AC power supply 15 is a normal value (100[V]), the peak voltage Vp
that is output from the voltage detection circuit 70 is 0.9[V], as
shown in FIG. 9. For this reason, in the case of the condition A
(the frequency of the pulse signal Sp is 100 Hz), the threshold is
set to be 1.5[V].
[0086] Also, in the case of a condition B, when the power supply
voltage of the AC power supply 15 is a normal value (100[V]), the
peak voltage Vp that is output from the voltage detection circuit
70 is 1.1[V], as shown in FIG. 10. For this reason, in the case of
the condition B (the frequency of the pulse signal Sp is 120 Hz),
the threshold is set to be 1.6[V].
[0087] Also, in the case of a condition C, when the power supply
voltage of the AC power supply 15 is a normal value (100[V]), the
peak voltage Vp that is output from the voltage detection circuit
70 is 1.8[V], as shown in FIG. 11. For this reason, in the case of
the condition C (the frequency of the pulse signal Sp is 50 Hz),
the threshold is set to be 3[V].
[0088] Also, in the case of a condition D, when the power supply
voltage of the AC power supply 15 is a normal value (100[V]), the
peak voltage Vp that is output from the voltage detection circuit
70 is 2.2[V], as shown in FIG. 12. For this reason, in the case of
the condition D (the frequency of the pulse signal Sp is 60 Hz),
the threshold is set to be 3.2[V].
[0089] Here, the conditions A to D are as follows.
[0090] The condition A is a case where there is no frame ground and
the power supply frequency of the AC power supply 15 is 50 Hz.
[0091] The condition B is a case where there is no frame ground and
the power supply frequency of the AC power supply 15 is 60 Hz.
[0092] The condition C is a case where there is the frame ground
and the power supply frequency of the AC power supply 15 is 50
Hz.
[0093] The condition D is a case where there is the frame ground
and the power supply frequency of the AC power supply 15 is 60
Hz.
[0094] The circuit constants are as follows.
[0095] Capacitances of the capacitors C4, C5 are 3,300 [pF],
forward voltage drops of the diodes D4 to D6 are 0.6 [V],
resistance values of the resistance Ra and the resistance R5 are
3.3 [k.OMEGA.], a resistance value of the resistance R3 is 470
[k.OMEGA.], a resistance value of the resistance R4 is 4.7
[M.OMEGA. (megaohm)], a capacitance of the capacitor CB is 680
[.mu.F] and a zener voltage of the zener diode Dz is 5.6 [V].
[0096] In the printer 1, a correspondence table shown in FIG. 8,
i.e., a correspondence table in which the frequency of the pulse
signal Sp, which is output from the pulse signal output circuit 60,
and the threshold are associated with each other, is beforehand
stored in the relay control block B2 and the like and the threshold
for determining whether the AC input voltage is an overvoltage is
changed in correspondence to the frequency of the pulse signal Sp.
For this reason, it is possible to correctly determine whether the
AC input voltage is an overvoltage, irrespective of a difference of
the power supply frequency of the AC power supply 15. Also, it is
possible to correctly determine whether the AC input voltage is an
overvoltage, irrespective of whether there is the frame ground.
[0097] Incidentally, when the power supply frequency of the AC
power supply 15 is two types of 50 Hz and 60 Hz, the basic
frequency of the pulse signal Sp is two patterns of 50 Hz and 60
Hz. That is, 100 Hz is a double frequency of the basic frequency 50
Hz and 120 Hz is a double frequency of the basic frequency 60 Hz.
For this reason, as described above, to set the thresholds for each
of the four patterns of 50 Hz, 60 Hz, 100 Hz and 120 Hz means that
the threshold is set for each basic frequency and the threshold is
set depending on a frequency ratio to the basic frequency (the
power supply frequency of the AC power supply).
[0098] 4. Protection Sequence of Switching Power Supply
[0099] In the below, a protection sequence of the switching power
supply 20 that is executed by the control device 100 is described
with reference to FIG. 13. Incidentally, the protection sequence of
the switching power supply 20 starts when the power supply cable is
connected to an AC outlet and the AC power supply 15 is thus input.
Also, it is assumed that the relay 40 is at the off state and the
switching power supply 20 is disconnected from the AC power supply
15 at the time that the AC power supply 15 is input.
[0100] After the AC power supply 15 is input, the charging current
flows through the backup capacitor CB via the auxiliary power
supply circuit 50. For this reason, the voltage of the backup
capacitor CB is increased. Thereby, a line voltage (hereinafter, a
power supply voltage Vdd) of the output line Lo4 is increased.
Then, when the power supply voltage Vdd exceeds a minimum operating
voltage, the relay control block B2 starts up (starts up using the
backup capacitor CB as a power supply).
[0101] After the startup, the relay control block B2 compares the
power supply voltage Vdd and a predetermined voltage to thus
determine whether the power supply voltage Vdd is the predetermined
voltage or higher (S10). Incidentally, the predetermined voltage is
a voltage at which the respective circuits 60, 70, 80 normally
operate by using the backup capacitor CB as a power supply, and is
3.3V, for example.
[0102] When the power supply voltage Vdd is the predetermined
voltage or lower (NO in S10), the processing of S10 is again
executed. Therefore, a standby state of waiting for the power
supply voltage Vdd to exceed the predetermined voltage while
monitoring the power supply voltage Vdd is made.
[0103] When the AC power supply 15 is input, the backup capacitor
CB is charged as time goes by, so that the power supply voltage Vdd
exceeds the predetermined voltage. Then, `YES` is determined in the
processing of S10 and the processing shifts to S20.
[0104] After the processing shifts to S20, the relay control block
B2 monitors an input of the input port P3 and detects the frequency
of the pulse signal Sp that is output from the pulse signal output
circuit 60. After that, the processing shifts to S30. In S30, a
threshold for determining an overvoltage of the AC power supply 15
is set by the relay control block B2. Specifically, regarding the
frequency of the pulse signal Sp detected in S20, a threshold
corresponding to the frequency of the pulse signal Sp is selected
and set with reference to the correspondence table shown in FIG. 8.
For example, when the frequency detected in S20 is 100 Hz, the
threshold is set to be 1.5 [V].
[0105] When the processing of S30 is over, the processing shifts to
S40 and the relay control block B2 determines whether the AC power
supply is off or not. When the AC power supply is not off (the AC
power supply is off when the power supply cable is unplugged, for
example), the pulse signal Sp is input to the input port P3 of the
relay control block B2 at a predetermined period. On the other
hand, when the AC power supply 15 is off, the pulse signal Sp is
not input. For this reason, the relay control block B2 can
determine whether the AC power supply is off or not by detecting
whether the pulse signal Sp is input at a predetermined period.
[0106] When the AC power supply 15 is not off (S40: NO), the
processing shifts to S50 and the relay control block B2 compares
the peak voltage Vp, which is output from the voltage detection
circuit 70, and the threshold set in S30 to thereby determine
whether the AC input voltage from the AC power supply 15 is within
a normal range. That is, when the peak voltage Vp is lower than the
threshold, it is determined that the AC input voltage is within the
normal range. On the other hand, when the peak voltage Vp is the
threshold or higher, it is determined that the AC input voltage is
an overvoltage. Incidentally, the `overvoltage detection process`
of the invention is implemented by the processing of S50 that is
executed by the relay control block B2.
[0107] When it is determined that the AC input voltage is within
the normal range, the processing shifts to S60 and a driving signal
is output from the control port P5 of the relay control block B2 to
the relay driving circuit 80. Thereby, the forward current flows
through the driving coil 43 via the relay driving circuit 80 and
the relay 40 becomes on. Thereby, the switching power supply 20 is
connected to the AC power supply 15 and then starts up.
[0108] On the other hand, when it is determined that the AC input
voltage is an overvoltage, the processing again shifts to S40 and
it is determined whether the AC power supply is off. When the AC
power supply 15 is not off, the processing shifts to S50 and it is
determined whether the AC input voltage from the AC power supply 15
is within the normal range. For this reason, when the AC input
voltage is abnormal (overvoltage), the processing of S40 and S50 is
repeated. During the repetition, the relay 40 is kept at the off
state by the relay control block B2. That is, since the relay
control block B2 does not output the driving signal turning on the
relay 40 and keeps the relay 40 at the off state, it is possible to
prevent the overvoltage from being applied to the switching power
supply 20 from the AC power supply 15.
[0109] Incidentally, the processing of S40 and S50 that is executed
by the relay control block B2, i.e., the processing of repeatedly
executing the processing of S40 and S50 not to thus turn on the
relay until the overvoltage is not detected implements the `process
of keeping the switching unit at a cutoff state where the AC power
supply and the switching power supply are disconnected, when an
overvoltage is detected in the overvoltage detection process`.
[0110] When the AC input voltage from the AC power supply 15 is
returned to the normal, the determination result of S50 is YES and
the processing shifts to S60. When the processing shifts to S60, a
driving signal is output from the control port P5 of the relay
control block B2 to the relay driving circuit 80, as described
above. Thereby, the forward current flows through the driving coil
43 via the relay driving circuit 80 and the relay 40 becomes on.
For this reason, the switching power supply 20 is connected to the
AC power supply 15 and then starts up.
[0111] After the processing of S60, the processing shifts to S70
and the relay control block B2 determines whether the AC power
supply is off or not. When the AC power supply 15 is not off (S70:
NO), the processing shifts to S80.
[0112] When the processing shifts to S80, the relay control block
B2 compares the peak voltage Vp, which is output from the voltage
detection circuit 70, and the threshold set in S30 to thereby
determine whether the AC input voltage from the AC power supply 15
is within the normal range, like the processing of S50.
[0113] When it is determined that the AC input voltage is within
the normal range, the processing shifts to S70 and it is determined
whether the AC power supply is off or not. When the AC power supply
15 is not off, the processing shifts to S80. For this reason, when
the AC input voltage is normal, the processing of S70 and S80 is
repeated. During the repetition, the relay 40 is kept at the on
state by the relay control block B2.
[0114] When the AC input voltage becomes an overvoltage, a result
of the determination in S80 is NO. When a result of the
determination in S80 is NO, the processing shifts to S90. In S90, a
driving signal is output from the control port P6 of the relay
control block B2 to the relay driving circuit 80. Thereby, the
reverse current flows through the driving coil 43 via the relay
driving circuit 80 and the relay 40 becomes off. For this reason,
the switching power supply 20 is disconnected from the AC power
supply 15. Therefore, it is possible to protect the switching power
supply 20 from the overvoltage.
[0115] After the processing of S90, the processing returns to S40.
Thus, the relay control block B2 monitors the AC input voltage
while keeping the relay 40 at the off state. When the AC input
voltage returns to the normal range, the relay control block B2
again turns on the relay 40 and connects the switching power supply
20 to the AC power supply 15 (S60). The processing is repeated, so
that only when the AC input voltage is within the normal range
during the execution of the protection sequence, the switching
power supply 20 is connected to the AC power supply 15, and when
the AC input voltage is abnormal (overvoltage), the switching power
supply 20 is disconnected from the AC power supply 15.
[0116] The protection sequence of the switching power supply 20 is
over when the AC power supply 15 is off because the power supply
cable is unplugged, for example. That is, when the AC power supply
15 is off at the state where the relay 40 is off, a result of the
determination in S40 is NO and the series of processing is over.
Also, when the AC power supply 15 is off at the state where the
relay 40 is on, the relay 40 becomes off in S100 and then the
series of processing is over.
[0117] As described above, when the protection sequence is over,
the relay 40 becomes off. For this reason, when a next protection
sequence is executed as the AC power supply 15 is input, the relay
40 becomes off and the switching power supply 20 is not connected
to the AC power supply 15 until the relay control block B2
determines that the AC input voltage is normal.
[0118] 5. Advantages
[0119] In the power supply system S, when starting up the switching
power supply 20, the relay 40 is turned off in advance to
disconnect the switching power supply 20 from the AC power supply
15. Then, based on the detection value (in this example, the peak
value Vp of the voltage Vab between both ends of the detection
resistance Ra) of the voltage detection circuit 70, it is detected
whether the AC input voltage from the AC power supply 15 is an
overvoltage or not. When an overvoltage is not detected, the relay
40 is shifted to the on state, so that the switching power supply
20 is connected to the AC power supply 15 and thus the switching
power supply 20 starts up.
[0120] On the other hand, when an overvoltage is detected, the
relay 40 is kept at the off state and the switching power supply 20
is kept being disconnected from the AC power supply 15. At the time
that the overvoltage is not detected, the relay 40 is shifted to
the on state, so that the switching power supply 20 is connected to
the AC power supply 15 and thus the switching power supply 20
starts up. In this way, the overvoltage is not applied to the
switching power supply 20, so that the switching power supply 20
can be protected from the overvoltage.
[0121] Also, in the power supply system, the auxiliary power supply
circuit 50 is configured by the pair of coupling capacitors C4, C5
and the bridge-type rectification circuit 53 and thus the auxiliary
power supply circuit 50 has a relatively simple configuration.
Also, the voltage detection circuit 70 is configured by the
detection resistance Ra and the processing circuit 75 and thus has
a simple configuration, which has a cost merit. Also, the voltage
is detected in the peak hold circuit 78. For this reason, compared
to a configuration of calculating an average of the voltages, it is
possible to detect the AC input voltage from the AC power supply in
a short time.
Second Illustrative Embodiment
[0122] In the below, a second illustrative embodiment of the
invention will be described with reference to FIG. 14.
[0123] In the first illustrative embodiment, the voltage detection
circuit 70 is configured by the detection resistance Ra and the
processing circuit 75. The processing circuit 75 is configured by
the subtraction circuit 76, the amplification circuit 77 and the
peak hold circuit 78 and detects the peak value Vp of the voltage
Vab between both ends of the detection resistance Ra. In the second
illustrative embodiment, the peak hold circuit 78 is changed to an
averaging circuit 79 to thus detect an average value Vav of the
voltage Vab between both ends of the detection resistance Ra. Since
the average value Vav is less influenced by a noise than the peak
value Vp, it is possible to correctly determine whether the AC
input voltage from the AC power supply 15 is an overvoltage or
not.
Third Illustrative Embodiment
[0124] In the below, a third illustrative embodiment of the
invention will be described with reference to FIG. 15.
[0125] In the first illustrative embodiment, the voltage detection
circuit 70 is configured by the detection resistance Ra and the
processing circuit 75 and the voltage Vab between both ends of the
detection resistance Ra is measured to detect the voltage of the AC
power supply 15.
[0126] In the third illustrative embodiment, the configuration of
the voltage detection circuit 70 of the first illustrative
embodiment is changed. In the third illustrative embodiment, a
voltage detection circuit 150 is configured by a bridge-type
rectification circuit (four bridge-connected diodes D10 to D13)
160, a capacitor 170 and a comparison circuit 180. The bridge-type
rectification circuit 160 is connected to the AC power supply 15
and rectifies the AC voltage of the AC power supply 15 and the
charging current flows from the bridge-type rectification circuit
160 to the capacitor 170. The comparison circuit 180 compares a
voltage of the capacitor 170 with a threshold voltage and turns on
a light emitting diode LED2 when the voltage of the capacitor 170
exceeds the threshold voltage.
[0127] The light emitting diode LED2 configures a photo-coupler
together with a photo transistor PT2 connected to a detection port
P7 of the relay control block B2. Hence, when the light emitting
diode LED2 is turned on, the photo transistor PT2 becomes on
(becomes electrically conductive) and a level of the detection port
P7 becomes a low level. On the other hand, when the light emitting
diode LED2 is not turned on, the photo transistor PT2 becomes off
(is not electrically conductive), so that a level of the detection
port P7 becomes a high level.
[0128] When the voltage of the AC power supply 15 is within the
normal range, the voltage of the capacitor 170 is smaller than the
threshold, so that the light emitting diode LED2 is turned off and
the level of the detection port P7 becomes a high level. On the
other hand, when the voltage of the AC power supply 15 is an
overvoltage, the voltage of the capacitor 170 exceeds the
threshold, so that the light emitting diode LED2 is turned on and
the level of the detection port P7 becomes a low level. Therefore,
the relay control block B2 can determine whether the AC input
voltage from the AC power supply 15 is an overvoltage or not by
monitoring the level of the detection port P7.
[0129] Like the first illustrative embodiment, when starting up the
switching power supply 20, the relay 40 is turned off in advance to
disconnect the switching power supply 20 from the AC power supply
15. Then, by monitoring the level of the detection port P7, the
relay control block B2 determines whether the AC input voltage from
the AC power supply 15 is an overvoltage or not.
[0130] When the overvoltage is detected, the relay control block B2
keeps the relay 40 at the off state and keeps disconnecting the
switching power supply 20 from the AC power supply 15. After that,
at the time that the overvoltage is not detected, the relay 40 is
shifted to the on state, so that the switching power supply 20 is
connected to the AC power supply 15 and thus the switching power
supply 20 starts up. In this way, the overvoltage is not applied to
the switching power supply 20, so that the switching power supply
20 can be protected from the overvoltage.
[0131] Incidentally, since the voltage detection circuit 150
determines whether the AC power supply 15 is an overvoltage, based
on a charged voltage of the capacitor 170, it is not necessary to
switch the threshold, depending on the power supply frequency or
whether or not the frame ground. That is, the charged voltage of
the capacitor 170 depends on only the voltage of the AC power
supply 15 and does not depend on the power supply frequency or
whether or not the frame ground. For this reason, in the third
illustrative embodiment, the pulse signal output circuit 60 is
omitted.
Modifications to Illustrative Embodiments
[0132] The invention is not limited to the illustrative embodiments
described above and shown in the drawings. Following illustrative
embodiments may also be included in the technical scope of the
invention.
[0133] (1) In the first to third illustrative embodiments, the
power supply system S is used for the printer. However, the power
supply system can be applied to any electric device and the utility
of the power supply system S is not limited to the printer. For
example, the power supply system can be widely used for home
appliances such as a television, a video recorder and the like.
Also, although the electrophotographic printer has been exemplified
in the first to third illustrative embodiments, the invention can
be also applied to an inkjet printer.
[0134] (2) In the first to third illustrative embodiments, the
latching relay is used as the relay 40. However, a relay having no
latch function may be also used.
[0135] (3) In the first to third illustrative embodiments, the
backup capacitor CB has been exemplified as the electricity storage
unit. However, a secondary battery can be also used.
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